1. Field of the Invention
The present invention relates to a power tong for connecting and disconnecting wellbore tubulars and, more specifically, to apparatus and method for controlling a grip of each of a plurality of power jaws.
2. Background of the Invention
The speed of connecting and disconnecting hundreds of wellbore tubulars makes a great difference in the time required to drill and bring a well into production. For instance, it is normally necessary to insert and remove the drill several times during the drilling process wherein numerous connections of the wellbore tubulars have to be made or broken. Due to the high cost of drilling equipment, it is therefore desirable to be able to make or break a connection as quickly as possible to keep drilling costs as low as possible.
One apparatus known for making and breaking wellbore tubulars includes a frame that supports up to three power jaws and a power spinner each aligned vertically with respect to each other. An exemplary example of such an apparatus is disclosed in U.S. Pat. No. 5,386,746 and is incorporated herein by reference. Preferably such an apparatus should be able to spin one tubular with the power spinner at a relatively high speed but at a relatively low torque while holding another tubular fixed with one of the power jaws. The spin process continues until the two threaded tubulars shoulder up, e.g. until a pin shoulder engages the box shoulder. After shouldering up, the power spinner is stopped and two of the power jaws are used to apply high torque to the connection or joint in a well known manner so the joint is securely fastened and sealed. The application of high torque continues to rotate the tubulars with respect to each other but at a very low speed of rotation. However, once the tubulars are shouldered it is not necessary to rotate but a relatively small amount so the low speed of rotation does not slow the process down. Likewise when breaking out joints, two power jaws apply a high torque to initially break the connection. Then the power spinner spins one tubular with respect to another tubular held by a power jaw until the threaded connection is completely disconnected. In this manner, the connectors can be quickly made or broken to save considerable time and money while drilling a well.
It was found that with certain types of wellbore tubulars such as new types of wellbore tubulars, the two tubulars were not always shouldered up during the spinning process. Because the tubulars were not shouldered up during the spinning process, substantial additional rotation was required with the power jaws until the tubulars were properly tightened. Providing substantial additional rotation with power jaws tends to be a slow process. Locating the problem of not shouldering up is a difficult process which could result from many causes. For instance, due the vertically stacked nature of the power jaws and power spinner in conjunction with the drilling rig slips and elevator for holding the two tubulars there are many alignment factors that are difficult to isolate. Therefore, those skilled in the art will appreciate the present invention that addresses these and other problems.
The present invention provides for a power tong for making up and breaking out wellbore tubulars. The invention comprises a power spinner for spinning the wellbore tubulars and a plurality of power jaws. At least one of the plurality of power jaws is preferably operable for gripping a respective first of the wellbore tubulars with a first grip pressure. The power jaw holds the respective first of the wellbore tubulars when the power spinner is spinning a respective second of the wellbore tubulars. Each of the plurality of power jaws is preferably operable for gripping the wellbore tubulars with a second grip pressure for applying high torque to the wellbore tubulars. The second grip pressure is preferably greater than the first grip pressure. A grip control is preferably provided for controlling at least one of the plurality of power jaws for automatically producing the first grip pressure during the spinning by the power spinner.
In a presently preferred embodiment, the plurality of power jaws includes three vertically oriented power jaws and the power spinner is preferably vertically oriented with respect to the three vertically oriented power jaws. A control unit may be provided to produce a control signal to activate the power spinner. The grip control is preferably responsive to the control signal to automatically shift to the first grip pressure.
A pressure limiting valve for each power jaw may preferably be used for producing the first grip pressure. A grip cylinder is preferably used with each of the plurality of power jaws and the pressure limiting valve controls pressure to the grip cylinder to produce the first grip pressure. In a preferred embodiment, one pressure limiting valve is preferably responsive to air pressure for controlling a hydraulic pressure. A grip cylinder valve may be used for controlling pressure to the grip cylinder to produce the second grip pressure. A frame for supporting the power spinner and the plurality of power jaws is preferably provided.
In operation, a power spinner is provided for spinning a first wellbore tubular. At least one power jaw is utilized for gripping and holding in position a second wellbore tubular as the first wellbore tubular is spinning with respect to second wellbore tubular for making up or breaking out a threaded connection. The at least one power jaw holds the second wellbore tubular with a first grip pressure. At least two power jaws are utilized for applying high torque for a final making up or an initial breaking out of the threaded connection. The at least two power jaws grip respective of the first and second tubulars with a second grip pressure for applying high torque. A grip control circuit is provided such that the first grip pressure is reduced as compared to the second grip pressure whenever the power spinner is spinning the first wellbore tubular.
In a preferred embodiment, a power spinner control circuit is provided that produces a spin control signal. The spin control signal is utilized to produce the first grip pressure. A grip cylinder provided for the power jaw, and pressure to the grip cylinder is controlled in response to the spin control signal.
In more detail, a power tong for making up and breaking out wellbore tubulars is provided with a first power jaw having a first gripping cylinder, a second power jaw having a second gripping cylinder, and a third power jaw having a third gripping cylinder. The first gripping cylinder controls a grip of the first power jaw, the second gripping cylinder controls a grip of the second power jaw, and the third gripping cylinder controls a grip of the third power jaw. A power spinner is used for spinning one of the wellbore tubulars while at least one of the power jaws grips another of the wellbore tubulars. A spinner control circuit activates the power spinner. A gripping control circuit for controls one of the gripping cylinders. The gripping control circuit is preferably operable for applying a first pressure to at least two of the gripping cylinders during a high torque operation for the making up or breaking out. The gripping control circuit is preferably responsive to the spinner control circuit for producing a second pressure smaller than the first pressure when the power spinner is activated and for applying the second pressure to at least one of the first gripping cylinder and the second gripping cylinder and the third gripping cylinder.